1. Field of the Invention
This invention relates to high voltage power supplies, and more particularly to a regulated high voltage power supply of the type including a flyback transformer suitable for providing a highly regulated anode voltage to a cathode ray tube.
2. Description of the Prior Art
In many high voltage applications, it has been found that unregulated power supplies are incapable of preventing undesired operational fluctuations in the utilization device supplied thereby. For example, in cathode ray tube displays, an increase in the brightness level produces an image distortion known as "blooming" due to increased demand on the high voltage power supply and the resultant lower output voltage thereof. To overcome this drawback, many arrangements incorporate regulating devices. However, typically such devices have the disadvantage of requiring the dissipation of equivalent energy in the regulation device when the output power demand is low. Other prior art devices utilize free-running oscillators to drive a switch transistor, and such results in random interference beat patterns in the television picture since the power supply switching frequency is non-synchronous with the TV's fast scan rate. Other prior art supplies have limited regulation capability when used with unregulated B+ input. And still others operate at lower switching frequencies which limits the usefulness to lower resolution television displays.
It is, therefore, a principal object of the present invention to overcome the disadvantages attendant in the prior art approaches and to provide an improved high voltage power supply which, inter alia, uses fast scan synchronization of the power supply switching frequency; i.e., the power supply switching rate is synchronized with the fast scan pulses rate of the CRT. In the preferred mode, the power supply switching is synchronized with the CRT fast scan frequency. As pointed out previously, by synchronizing the switching rate to the CRT scan rate, random interference, beat patterns on the CRT display are avoided. By synchronizing regulator switching the effect of any switching transients on the CRT display are minimized. In addition, the power supply regulates the output by feedback to a device which regulates the B+ input.